The spectrum ranges from 3 Hz to 3 THz, and allocation within the spectrum is governed by the International Telecommunication Union (ITU). A band is considered a portion of the spectrum that can be allocated, licensed, sold, or freely used depending on the frequency. From an ITU perspective, the bands are categorized as follows:
Within the United States, the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) control the frequency spectrum usage rights. The FCC administrates the non-Federal spectrum usage, while the NTIA administers the Federal usage (army, FAA, ...
